This project is presently focused on the following problems: 1. The relationship between natural killing (NK) and activated lymphocyte killing (AK) against K562 and T cell lines, as contrasted against B-cell derived lines; 2. Interferon activation of cytotoxicity (IAK) a) differential sensitivity of different established lines; b) preferential killing of allogenic, compared to autologous tumor biopsy cells. 3. The natural attachment (NA) phenomenon. 4. The increase of the NK-sensitivity of EBV carrying cells upon their entry into the viral cycle.